In-frame multi-exon deletion of SMC1A in a severely affected female with Cornelia de Lange Syndrome.

Cornelia de Lange Syndrome (CdLS) is a genetically heterogeneous disorder characterized by dysmorphic facial features, cleft palate, limb defects, growth retardation, and developmental delay. Approximately 60% of patients with CdLS have an identifiable mutation in the NIPBL gene at 5p13.2. Recently, an X-linked form of CdLS with a generally milder phenotype was attributed to mutation of the structural maintenance of chromosomes 1A gene (SMC1A) at Xp11.22. Relatively few CdLS patients with mutations in SMC1A are known; female carriers have minor facial dysmorphism and cognitive deficiency without major structural abnormalities. To date, all mutations identified in SMC1A are missense or small in-frame deletions that preserve the open reading frame of the gene and likely have a dominant-negative effect. We report on a female with monosomy X mosaicism and a phenotype suggestive of a severe form of CdLS who presented with growth and mental retardation, multiple congenital anomalies, and facial dysmorphism. Array CGH confirmed mosaic monosomy X and identified a novel deletion of SMC1A spanning multiple exons, suggesting a possible loss-of-function effect. Sequencing of both genomic and cDNA demonstrated an 8,152 bp deletion of genomic DNA from exon 13 to intron 16. Although a loss-of-function effect cannot be excluded, the resulting mRNA remains in-frame and is expressed in peripheral blood lymphocytes, suggesting a dominant-negative effect. We hypothesize that the size of this deletion compared to previously reported mutations may account for this patient's severe CdLS phenotype. The presence of mosaic monosomy X may also modify the phenotype.

Evaluation of oligonucleotide sequence capture arrays and comparison of next-generation sequencing platforms for use in molecular diagnostics.

BACKGROUND: Next-generation DNA sequencing (NGS) techniques have the potential to revolutionize molecular diagnostics; however, a thorough evaluation of these technologies is necessary to ensure their performance meets or exceeds that of current clinical sequencing methods. METHODS: We evaluated the NimbleGen Sequence Capture 385K Human Custom Arrays for enrichment of 22 genes. We sequenced each sample on both the Roche 454 Genome Sequencer FLX (GS-FLX) and the Illumina Genome Analyzer II (GAII) to compare platform performance. RESULTS: Although the sequence capture method allowed us to rapidly develop a large number of sequencing assays, we encountered difficulty enriching G+C-rich regions. Although a high proportion of reads consistently mapped outside of the targeted regions, >80% of targeted bases for the GAII and >30% of bases for the GS-FLX were covered by a read depth of > or =20, and > 90% of bases for the GAII and > 80% of bases for the GS-FLX were covered by a read depth of > or =5. We observed discrepancies among sequence variants identified by the different platforms. CONCLUSIONS: Although oligonucleotide arrays are quick and easy to develop, some problematic regions may evade capture, necessitating sequential redesigning for complete optimization. Neither sequencing technology was able to detect every variant identified by Sanger sequencing because of well-known drawbacks of the NGS technologies. The rapidly decreasing error rates and costs of these technologies, however, coupled with advancing bioinformatic capabilities, make them an attractive option for molecular diagnostics in the very near future.

Partial hexasomy for the Prader-Willi-Angelman syndrome critical region due to a maternally inherited large supernumerary marker chromosome.

Extra copies of the Prader-Willi-Angelman syndrome critical region (PWASCR) have been shown to have detrimental phenotypic effects depending on the parent of origin. Hexasomy for the PWASCR is rare; only 6 cases have been described to date. We report on a 15-year-old girl referred for developmental delay and seizures with a mosaic tricentric small marker chromosome (SMC) 15 identified by routine G-banding chromosome studies. C-banding and FISH confirmed the presence of three chromosome 15 centromeres as well as four copies of the PWASCR on the SMC in approximately 60% of interphase cells. Microsatellite genotyping documented maternal inheritance of the SMC, and methylation-sensitive multiplex ligation-dependent PCR amplification (MS-MLPA) showed that the extra copies of the PWASCR contained on the marker chromosome bear a methylation pattern similar to a normal maternal chromosome, implying maternal inheritance. These findings are consistent with the patient's phenotype as paternal inheritance of such a marker chromosome is thought to be benign. However, this patient's phenotype is the mildest described to date and may be a result of mosaicism for the SMC.

Expanding DNA diagnostic panel testing: is more better?

During the last 25 years, a small number of meaningful DNA-based diagnostic tests have been available to aid in the diagnosis and subsequent treatment of heritable disorders. These tests have targeted a limited number of genes and are often ordered in serial testing strategies in which results from one preliminary test dictate the subsequent test orders. This approach can be both time and resource intensive when a patient requires several genes to be sequenced. Recently, there has been much discussion regarding how 'massively parallel' or 'next-generation' DNA sequencing will impact clinical care. While the technology promises to reduce the cost of sequencing an entire human genome to less than US$1000, one must question the diagnostic utility of complete genome sequencing for routine clinical testing, given the many interpretive challenges posed by this approach. At present, it appears next-generation DNA sequencing may provide the greatest benefit to routine clinical testing by enabling comprehensive multigene panel sequencing. This should provide an advantage over traditional Sanger-based sequencing strategies while limiting the total test output to sets to genes with known diagnostic value. This article will discuss the current and near future state of clinical testing approaches and explore what challenges must be addressed in order to extract diagnostic value from whole-exome sequencing and whole-genome sequencing, using hereditary colon cancer as an example.

Identification of a patient with 7q32 deletion-associated acute myeloid leukemia and an incidental t(8;14).

Constitutional activation of the MYC proto-oncogene resulting from a t(8;14) has been demonstrated in approximately 80% of Burkitt lymphoma patients, but only in one case of acute myeloid leukemia (AML). We report on a 59-year-old female diagnosed with minimally differentiated AML (M0). Chromosome analysis demonstrated both a 7q deletion and a t(8;14). Fluorescence in situ hybridization studies confirmed MYC/IGH fusion in 35% of nuclei, but the translocation was atypical due to lack of immunoglobulin heavy chain (IGH) gene disruption. Such an atypical fusion has never been reported, so the effect on MYC regulation due to proximity of IGH regulatory elements is unknown. Real-time polymerase chain reaction analysis demonstrated no increase in MYC expression (P = 0.12). These results suggest that this novel translocation does not result in dysregulation of MYC expression, so this is likely to be a coincidental, benign finding in this patient. This is yet another example of a classic cytogenetic abnormality observed on conventional chromosome analysis which has no functional significance.